The present invention relates generally to Schottky barrier diodes, and more specifically to an ion implanted Schottky barrier diode.
Generally, Schottky barrier diodes are fabricated in low concentration N-type material, for example, 0.1 to 0.2 ohm-centimeters. An example of the prior art for the simultaneous formation of Schottky barrier diodes with P-type guard rings and a Schottky clamped NPN bipolar transistor is described in U.S. Pat. No. 4,035,907. The starting material is an N epitaxial material of the appropriate impurity concentration to produce the low resistivity starting material. Another example is U.S. Pat. No. 3,846,192 wherein the formation of an NPN bipolar transistor and Schottky diodes of two different thresholds are formed by selective N-type diffusion into an N epitaxial layer having a low resistance of 0.8 ohm-centimeters. The use of ion implantation to form an N.sup.- region capable of forming a Schottky barrier is illustrated in U.S. Pat. No. 4,099,260. N-type impurities are ion implanted and diffused into a P-type substrate. Ion implantation has also been used to form a shallow surface layer of a higher impurity level than the bulk semiconductor body portion of Schottky barrier device to control the height of the barrier. This is illustrated in U.S. Pat. No. 4,045,248.
Linear type integrated circuits to provide high voltage complementary bipolar transistors generally use an N-type starting material having a bulk resistance in the range of three to twenty ohm-centimeters. The starting material is unsuitable for the formation of acceptable or useful Schottky barrier diodes. The prior art discussed above generally deals with the formation of Schottky barrier diodes and the possible formation of additional devices therewith. Thus, they have started with an appropriately low resistive material to assure the formation of the Schottky barrier diode. Starting with high resistive starting material required for high voltage complementary bipolar transistors, a way must be found to modify the starting material so as to produce useful Schottky barrier diodes. The criteria for useful Schottky barrier diodes is that the forward voltage be lower than a diffused PN junction diode, it should have a low reverse leakage, it should have a low series resistance, and it should have a sufficient reverse breakdown.